1. Field of the Invention
The present invention relates to a method for orienting a liquid crystal and a liquid crystal display device, and more particularly, to a method for orienting a liquid crystal appropriate for a liquid crystal display device which is combined with an amorphous silicon function element, and a liquid crystal display device.
2. Description of the Prior Art
Heretofore there have been known display devices having a driving switching element array, for example, an example of the display devices is disclosed in IEEE Transactions on Electron Devices ED-20, p. 995 (1973).
Where a large type of display panel provided with function elements of amorphous silicon (hereinafter referred to as "a-Si") as switching elements is used for utilizing a liquid crystal mode showing a display effect by the orientation substantially perpendicular to the substrate, the following orientation treating conditions should be satisfied.
In particular, orientation methods appropriate for a display device provided with a thin film transistor array having on the surface at least two different functions and at least two different materials should satisfy the following conditions.
(1) When an electric field is applied, the tilting direction is uniform. And substantially homeotropic alignment is obtained. PA0 (2) The a-Si is not affected by heat. PA0 (3) The a-Si is not contaminated with impurities. PA0 (4) Uniform orientation can be effected over a large area. PA0 (1) A method where a substrate surface itself washed with an acid or alkali is used as an active surface. PA0 (2) A method where the surface is treated by a physical method such as rubbing, oblique evaporation deposition, etching and the like. PA0 (3) A method where an orientation agent such as lecithin, various polymers, surfactants and the like is formed as a film. PA0 (4) A method where an orientation agent such as a fatty acid, a surfactant containing a quarternary amine and the like is added to a liquid crystal.
Furthermore, the orientation treating method should be that which is reliable, inexpensive and appropriate for mass treatment.
Many orientation methods for liquid crystal display devices have been proposed and these orientation methods are all concerned with an action at the interface between the liquid crystal and the electrode substrate. These methods may be roughly classified as shown below.
However, conventional orientation methods are not appropriate for the above mentioned large type of display panel haing a-Si function elements as the switching element.